Parasitoid Wasp Sampling for the Study of Polydnavirus Evolution

Kat Terwelp, Harrison C Moss, Lindsay Ackerman, Meredith Cobb, Alexis Yoh

Abstract

Polydnaviruses (PDVs) are a group of obligate symbiotic viruses associated with certain species of parasitoid wasps within the Ichneumonoidea superfamily. The virus is delivered with the wasp eggs during oviposition and PDV gene expression is required for successful parasitization of the secondary host. Members of a PDV multigene family called vinnexins, which are homologues of the insect Innexin gap junction gene family, are postulated to alter cellular communication, supporting a successful parasitization. We hypothesize that vinnexin family members are present in all ichneumonid family-associated PDVs, and that variation in gene complement, transcript pattern, and protein function is associated with differential host susceptibility. To test this hypothesis, we are collecting and preserving insects in South Carolina, Wisconsin and Ohio. We have developed a bifurcating key to identify and preserve parasitoid wasps. From these we will identify campoplegine and banchine wasps, which are associated with PDVs, and isolate DNA. Using DNA we will identify species, and isolate wasp innexins as well as vinnexins, then perform molecular evolutionary analyses. This study will assist in determining the relationship of PDV-gene family evolution with the diversity of their wasp symbionts. Additionally, insect specimens will be donated to museums aiding in biodiversity studies.

Illustrated Abstract

Polydnaviruses (PDVs) are a group of obligate symbiotic viruses associated with certain species of parasitoid wasps within the Ichneumonoidea superfamily. Each wasp species contains genetically unique PDV integrated into their genome and an encapsidated form of PDV that replicates in their reproductive tract. When the wasp lays their eggs into the Lepidopteran host, it also injects PDV particles which disable the host’s immune system (1). The wasp eggs hatch and the pupa eat the host alive.

Innexins are four-pass transmembrane proteins with N- and C-termini in the cytoplasm. They also have two extracellular and one intracellular loops. The hexamerization of Innexins forms a hemichannel. As part of the cellular membrane, hemichannel interaction between two cells can form a gap junction (2).

Results

LocationTime PeriodTotalHymenoptera
Clemson, South CarolinaJuly 21-August 11901221
Tamasse, South CarolinaJuly 25-August 852824
Wauwatosa, WisconsinJune 16-July 312214110
Port Clinton, OhioJuly 23-August 11109524

Insects were taken from the collecting bottle from the malaise trap. The total number of insects were counted and Hymenoptera were identified and separated based on phenotypic differences. A Lightview Pro LED magnifying lamp was used to distinguish between smaller insects. The total number of Hymenoptera was counted and stored in a container of PEG for further analysis. Methods of separating Hymenoptera were not equal between trap sites so the number of Hymenoptera cannot be compared.

Materials and Methods

There were four sites:
Clemson, South Carolina
Tamasse, South Carolina
Wauwatosa, Wisconsin
Port Clinton, Ohio

  1. Set up Malaise Trap
  2. Gather insects in a collection jar
  3. Sort insects into bycatch or catch
    • Type of wings, looking for parchment-like (remove any beetles with hardened/leathery wings or Lepidoptera with scaly wings)
    • Number of wings (remove any Diptera or insects with 2 wings)
    • Body shape (base of the abdomen is strongly constricted, like a waist)
    • Wing venation (horse head wing venation indicate Ichneumonid wasps)

Insects were sorted based on wingtype (parchment-like, leathery, or scaly), the number of wings, body shape, and wing venation. The horse-head venation at the bottom is a feature of Ichneumonid wasps.

Conclusions

Next Steps

  • Sort out Ichneumonids
  • ID campoplegine and bachine wasps
  • Isolate DNA and ID species
  • Isolate wasp innexins and vinnexins
  • Molecular evolutionary analysis 
  • Donate bycatch

References

  1. Turnbull,M.W.,Volkoff, A.-N.,Webb, B.A.,Phelan, P., 2005. Functional gap-junction genes are encoded by insect viruses. Curr Biol 15, R491-492
  2. Burke, G. R., & Strand, M. R. (2012). Polydnaviruses of Parasitic Wasps: Domestication of Viruses To Act as Gene Delivery Vectors. Insects, 3(1), 91–119. https://doi.org/10.3390/insects3010091